1. Field of the Invention
This invention relates generally to fittings for use in connecting tubing and other components of gas chromatography, liquid chromatography, in vitro diagnostic analysis systems, environmental (water) analysis systems, and other analytical systems, and relates more particularly to torque limited fittings.
2. Description of the Related Art
Liquid chromatography (LC), ion chromatography (IC) and gas chromatography (GC) are well-known techniques for separating the constituent elements in a given sample. In a conventional LC system, a liquid solvent (referred to as the “mobile phase”) is introduced from a reservoir and is pumped through the LC system. The mobile phase exits the pump under pressure. The mobile phase then travels via tubing to a sample injection valve. As the name suggests, the sample injection valve allows an operator to inject a sample into the LC system, where the sample will be carried along with the mobile phase.
In a conventional LC system, the sample and mobile phase pass through one or more filters and often a guard column before coming to the column. A typical column usually consists of a piece of tubing which has been packed with a “packing” material. The “packing” consists of the particulate material “packed” inside the column. It usually consists of silica- or polymer-based particles, which are often chemically bonded with a chemical functionality. When the sample is carried through the column (along with the mobile phase), the various components in the sample migrate through the packing within the column at different rates (i.e., there is differential migration of the solutes). In other words, the various components in a sample will move through the column at different rates. Because of the different rates of movement, the components gradually separate as they move through the column. Differential migration is affected by factors such as the composition of the mobile phase, the composition of the stationary phase (i.e., the material with which the column is “packed”), and the temperature at which the separation takes place. Thus, such factors will influence the separation of the sample's various components.
Once the sample (with its components now separated) leaves the column, it flows with the mobile phase past a detector. The detector detects the presence of specific molecules or compounds. Two general types of detectors are used in LC applications. One type measures a change in some overall physical property of the mobile phase and the sample (such as their refractive index). The other type measures only some property of the sample (such as the absorption of ultraviolet radiation). In essence, a typical detector in a LC system can measure and provide an output in terms of mass per unit of volume (such as grams per milliliter) or mass per unit of time (such as grams per second) of the sample's components. From such an output signal, a “chromatogram” can be provided; the chromatogram can then be used by an operator to determine the chemical components present in the sample. Additionally, LC systems may utilize mass spectrometric detection for identification and quantification of the sample, either in addition to, or as an alternative to, the conventional detectors described previously. Ion chromatography relies on the detection of ions in solution, so most metallic materials in the flow path can create interference in the detection scheme, as they create background ions.
In addition to the above components, a LC system will often include filters, check valves, a guard column, or the like in order to prevent contamination of the sample or damage to the LC system. For example, an inlet solvent filter may be used to filter out particles from the solvent (or mobile phase) before it reaches the pump. A guard column is often placed before the analytical or preparative column; i.e., the primary column. The purpose of such a guard column is to “guard” the primary column by absorbing unwanted sample components that might otherwise bind irreversibly to the analytical or preparative column.
In practice, various components in an LC system may be connected by an operator to perform a given task. For example, an operator will select an appropriate mobile phase and column, and then connect a supply of the selected mobile phase and a selected column to the LC system before operation. In order to be suitable for LC applications, each connection must be able to withstand the typical operating pressures of the LC system. If the connection is too weak, it may leak. Because the types of solvents that are sometimes used as the mobile phase are often toxic and because it is often expensive to obtain and/or prepare many samples for use, any such connection failure is a serious concern.
It is fairly common for an operator to disconnect a column (or other component) from a LC system and then connect a different column (or other component) in its place after one test has finished and before the next begins. Given the importance of leak-proof connections in LC applications, the operator must take time to be sure the connection is sufficient. Replacing a column (or other component) may occur several times in a day. Moreover, the time involved in disconnecting and then connecting a column (or other component) is unproductive because the LC system is not in use and the operator is engaged in plumbing the system instead of preparing samples or other more productive activities. Hence, the replacement of a column in a conventional LC system involves a great deal of wasted time and inefficiencies.
Given concerns about the need for leak-free connections, conventional connections have been made with stainless steel tubing and stainless steel end fittings. More recently, however, it has been realized that the use of stainless steel components in a LC system have potential drawbacks in situations involving biological samples, and cannot be routinely used for ion chromatography. For example, the components in a sample may attach themselves to the wall of stainless steel tubing. This presents problems because the detector's measurements (and thus the chromatogram) of a given sample may not accurately reflect the sample if some of the sample's components or ions remain in the tubing and do not pass the detector. Perhaps of even greater concern, however, is the fact that ions from the stainless steel tubing may detach from the tubing and flow past the detector, thus leading to potentially erroneous results. Hence, there is a need for “biocompatible” or “metal-free” connections through the use of a material that is chemically inert with respect to such “biological” samples and the mobile phase used with such samples, so that ions will not be released by the tubing and thus contaminate the sample.
In many applications using selector/injector valves to direct fluid flows, and in particular in liquid chromatography, the volume of fluids is small. This is particularly true when liquid chromatography is being used as an analytical method as opposed to a preparative method. Such methods often use capillary columns and are generally referred to as capillary chromatography. In capillary chromatography, it is often desired to minimize the internal volume of the selector or injector valve. One reason for this is that a valve having a large volume will contain a relatively large volume of liquid, and when a sample is injected into the valve the sample will be diluted, decreasing the resolution and sensitivity of the analytical method.
Micro-fluidic analytical processes also involve small sample sizes. As used herein, sample volumes considered to involve micro-fluidic techniques can range from as low as volumes of only several picoliters or so, up to volumes of several milliliters or so, whereas more traditional LC techniques, for example, historically often involved samples of about one microliter to about 100 milliliters in volume. Thus, the micro-fluidic techniques described herein involve volumes one or more orders of magnitude smaller in size than traditional LC techniques. Micro-fluidic techniques can also be expressed as those involving fluid flow rates of about 0.5 ml/minute or less.
As noted, liquid chromatography (as well as other analytical) systems typically include several components. For example, such a system may include a pump; an injection valve or autosampler for injecting the analyte; a precolumn filter to remove particulate matter in the analyte solution that might clog the column; a packed bed to retain irreversibly adsorbed chemical material; the LC column itself; and a detector that analyzes the carrier fluid as it leaves the column. Ion chromatography may also utilize a suppressor column to facilitate detection dynamic range. These various components may typically be connected by a miniature fluid conduit, or tubing, such as metallic or polymeric tubing (for ion chromatography), usually having an internal diameter of 0.003 to 0.040 inch.
All of these various components and lengths of tubing are typically interconnected by threaded fittings. Fittings for connecting various LC system components and lengths of tubing are disclosed in prior patents, for example, U.S. Pat. Nos. 5,525,303; 5,730,943; and 6,095,572, the disclosures of which are herein all incorporated by reference as if fully set forth herein. Often, a first internally threaded fitting seals to a first component with a ferrule or similar sealing device. The first fitting is threadedly connected through multiple turns by hand or by use of a wrench or wrenches to a second fitting having a corresponding external fitting, which is in turn sealed to a second component by a ferrule or other seal. Disconnecting these fittings for component replacement, maintenance, or reconfiguration often requires the use of a wrench or wrenches to unthread the fittings. Although a wrench or wrenches may be used, other tools such as pliers or other gripping and holding tools are sometimes used. In addition, the use of such approaches to connect components of an LC system often results in deformation or swaging of a ferrule used to provide a leak proof seal of tubing to a fitting or component. This often means that the ferrule and tubing connection, once made, cannot be reused without a risk of introducing dead volumes into the system. In addition, such approaches may involve crushing or deformation of the inner diameter of the tubing, which may adversely affect the flow characteristics and the pressures of the fluid within the tubing.
Another approach to provide a connection in an LC system involves providing a fitting assembly that uses a combination of components, including two separate ferrules. Such an approach is considered undesirable because by requiring two places for the ferrules to provide leak proof seals, it provides two places where the fluid to be analyzed may leak, as well as where dead volumes may be provided. In addition, this approach involves the use of additional components, which can cost more and also increase the time and effect to assemble them to make a connection or disassemble them when disconnecting tubing from a component or other fitting assembly.
There exists a need for fluidic fittings that are more reliable and have increased performance, which can be accomplished by applying a specific amount of torque to a fluidic fitting. The long used standard of “finger tight” when applying torque introduces a great deal of variation into the process. This results in fittings being under tightened, which causes leaks, or potentially over-tightened (with a tool), which can result in damage to fittings and ports. In general a torque limiting fitting would be preferred over the use a torque tool (such as a torque wrench) since torque tools require specific designs to allow access to specific fittings, employee training, additional assembly time, and associated costs (e.g., tool purchase and periodic calibration). Preferably a torque limiting fitting would look and feel like a standard fitting, but reliably and accurately assemble to the correct torque without influence from the user. It would also be required to disassemble like a standard fitting as well.
U.S. Pat. No. 5,183,140 discloses a general torque limiting mechanism, which comprises two rotatable members, one of which is the driving member and the other of which is the driven member. One of the members includes a single radial projection extending from a central hub that engages a recessed area on the other member. Below the torque limit the projection engages the recessed area and allows the driving member to drive the driven member, but above the torque limit the projection disengages the recessed area and prohibits the driving member from driving the driven member. U.S. Pat. No. 7,984,933 discloses a torque limiting fitting, which also comprises two rotatable members, one of which is the driving member and the other of which is the driven member. One of the members includes a lever extending from a central hub that engages an abutment on the other member. Below the torque limit the lever engages the abutment and allows the driving member to drive the driven member, but above the torque limit the lever deflects from the abutment and prohibits the driving member from driving the driven member. However the radial projection and the lever are only supported on one end, which can result in inconsistency in the torque limit and generally lower maximum torque values.
It will be understood by those skilled in the art that, as used herein, the term “LC system” is intended in its broad sense to include all apparatus and components in a system used in connection with a liquid chromatography system, and that the discussion of fittings in the context of LC systems is exemplary, as the invention may apply beyond LC systems to gas and ion chromatography, as well as or in vitro diagnostic or environmental analysis, and in other analytical instruments and systems, and may be made of only a few simple components or made of numerous, sophisticated components which are computer controlled or the like. Those skilled in the art will also appreciate that an LC system is one type of an analytical instrument (AI) system. For example, gas chromatography is similar in many respects to liquid chromatography, but obviously involves a gas sample to be analyzed. Although the following discussion focuses on liquid chromatography, those skilled in the art will appreciate that much of what is said with respect to LC systems also has application to other types of AI systems and methods.
Therefore, it is an object of the present invention to provide a torque limited fitting for use in an LC or other AI system.
It is another object of the present invention to provide a torque limited fitting that can be reusable about 5 to 10 times or more.
It is another object of the present invention to provide a torque limited fitting that performs like a regular fitting.
It is another object of the present invention to provide a mechanism allowing an operator to quickly disconnect or connect tubing or other component of an LC or other AI system.
It is another object of the present invention to provide a mechanism to reduce inefficiency and wasted time in connecting or disconnecting tubing or other component of an LC or other AI system.
It is yet another object of the present invention to provide a mechanism to allow an operator to quickly replace tubing or other component of an LC or other AI system.
It is yet another object of the present invention to provide a mechanism to allow an operator to quickly and easily achieve a leak-free connection of tubing or other component of an LC or other AI system by hand.
It is still another object of the present invention to provide a torque limited fitting to minimize the risk of leakage or damage to the tubing of an LC system.
It is still another object of the present invention to provide a biocompatible torque limited fitting to allow an operator to quickly and easily achieve a biocompatible connection of tubing or other component of an LC or other AI system.
It is still another object of the present invention to provide a “metal-free” torque limited fitting to allow an operator to quickly and easily achieve a metal-free connection of tubing or other component of an LC or other AI system.
The above and other advantages of the present invention will become readily apparent to those skilled in the art from the following detailed description of the present invention, and from the attached drawings, which are briefly described below.